The present application relates to a microchip and a channel structure for the same. More particularly, the invention relates, for example, to a microchip which is provided with a channel or channels for performing chemical and biological analyses and in which liquid feeding is conducted in the condition where a laminar flow of a sample liquid is surrounded by a laminar flow of a sheath liquid in the channels.
In recent years, microchips have been developed in which an area and/or a channel or channels for performing chemical and biological analyses are provided by application of micro-machining techniques used in the semiconductor industry. These microchips have begun to be utilized for electrochemical detectors in liquid chromatography, small electrochemical sensors in medical service sites, and the like.
Analytical systems using such microchips are called μ-TAS (micro-Total-Analysis System), lab-on-a-chip, bio chip or the like, and is paid attention to as a technology by which chemical and biological analyses can be enhanced in speed, efficiency and level of integration or by which analyzing apparatuses can be reduced in size.
The μ-TAS, which enables analysis with a small amount of sample and enables disposable use of microchips, is expected to be applied particularly to biological analyses where precious trace amounts of samples or a multiplicity of specimens are treated.
An application example of the μ-TAS is a particulate analyzing technology in which characteristics of particulates such as cells and microbeads are analyzed optically, electrically or magnetically in channels arranged on microchips. In the particulate analyzing technology, fractional collection of a population satisfying a predetermined condition or conditions from among particulates on the basis of analytical results of the particulates is also conducted.
For example, Japanese Patent Laid-open No. 2003-107099 (hereinafter referred to as Patent Document 1) discloses “a particulate fractionation microchip having a channel for introducing particulate-containing solution, and a sheath flow forming channel arranged on at least one lateral side of the introducing channel.” The particulate fractionation microchip further has “a particulate measuring section for measuring the particulates introduced, at least two particulate fractionating channels disposed on the downstream side of the particulate measuring section so as to perform fractional collection of the particulates, and at least two electrodes disposed in the vicinity of channel ports opening from the particulate measuring section into the particulate fractionating channels so as to control the moving direction of the particulates.”
The particulate fractionation microchip disclosed in Patent Document 1, typically, is so designed that fluid laminar flows are formed by a “trifurcated channel” having a channel for introducing a particulate-containing solution and two sheath flow forming channels (see “FIG. 1” of the document).
FIGS. 13A and 13B show an ordinary trifurcated channel structure (FIG. 13A), and sample liquid and sheath laminar flows (FIG. 13B) formed by the channel structure. In the trifurcated channel, a sample liquid laminar flow passing through a channel 101 in the direction of solid-line arrow in FIG. 13A can be sandwiched, from the left and right sides, by sheath liquid laminar flows introduced through channels 102, 102 in the directions of dotted-line arrows in the figure. By this, as shown in FIG. 13B, the sample liquid laminar flow can be fed through the center of the channel. Incidentally, in FIG. 13B, the sample liquid laminar flow is depicted in solid lines, and the channel structure in dotted lines.
In the particulate fractionation microchip disclosed in Patent Document 1, the trifurcated channel ensures that the particulate-containing solution is sandwiched by the flows of the sheath liquid from the left and right sides, and the particulates are made to flow through the center of the channel in the particulate measuring section. As a result, in the case of measuring the particulates optically, for example, each of the particulates can be accurately irradiated with measuring light.